Conventional imaging photodetection devices are disclosed for example by Non-patent document 1 and Non-patent document 2. The imaging photodetection devices disclosed thereby will be described below in brief.
FIG. 9A is a side view showing a schematic configuration of a conventional imaging device. Alight beam such as natural light enters an object 1, and the light beam reflected thereby forms an image 3 on a photodetection device 4 such as CCD or CMOS by a lens system 2. Though the lens system 2 is composed typically by combining a plurality of lenses aligned along an optical axis in order to ensure the optical performance, the lens system 2 is shown schematically as a single lens in FIG. 9A.
FIG. 9B is a view showing a schematic configuration of the photodetection device 4, and it is a magnified cross-sectional view of a portion 9B in FIG. 9A. A low refractive index transparent buffer layer 7 made of SiO2 or the like, a high refractive index transparent buffer layer 8 made of SiN or the like, a plurality of color filters 9 and a plurality of microlenses 10 are laminated in this order on a detection substrate 5 where a plurality of photodetectors 6 have been formed. An uneven structure is provided on a surface 7a of the transparent buffer layer 7 in contact with the transparent buffer layer 8 so that the thickness of the transparent buffer layer 7 is decreased at each of the photodetectors 6. In contrast, a surface 8a of the transparent buffer layer 8 in contact with the color filters 9 is shaped flat.
The microlenses 10 are arranged at the respective intersections of an orthogonal grid, and one color filter 9 and one photodetector 6 are arranged on the central axis of each microlens 10.
The microlenses 10 function for refracting light such as a light beam 11a′ that enters with a shift relative to the central axis of the microlens 10 and guiding the light to the photodetector 6. The uneven structure on the surface 7a of the transparent buffer layer 7 also has a lens effect, thereby refracting a divergent light beam 11b′ that travels in a direction away from the center of the photodetector 6 and guiding it to the photodetector 6.
The color filters 9 are composed of three kinds of filters, namely, a red transmission filter 9R, a green transmission filter 9G and a blue transmission filter 9B. The red transmission filter 9R has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of wavelength other than red, as illustrated with a curve R in FIG. 10; the green transmission filter 9G has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of wavelength other than green, as illustrated with a curve G in FIG. 10; and the blue transmission filter 9B has a light transmission characteristic (spectral sensitivity characteristic) of cutting (absorbing) light of wavelength other than blue, as illustrated with a curve B in FIG. 10 (see Non-patent document 2). One pixel for detecting color image information is configured with four color filters 9 composed of the red transmission filter 9R, the green transmission filter 9G, the blue transmission filter 9B, and a green transmission filter 9G for brightness detection, and also four photodetectors 6 corresponding to the color filters 9.
FIG. 11 is a magnified plan view of a detection plane of the optical detection device 4. The photodetectors 6 are arranged at the intersections of the orthogonal grid in a state spaced and insulated from each other. Between the photodetectors 6 adjacent horizontally to each other, a plurality of vertical transfer CCDs 17 as signal wirings extending vertically are provided, and the plural vertical transfer CCDs 17 are connected to a horizontal transfer CCD 18 as a signal wiring extending horizontally. Light focused by the microlens 10 is received by the photodetector 6 located just under the microlens 10, and photoelectrically converted. Electric charge stored in the photodetector 6 is sent to the vertical transfer CCDs 17 and further sent to the horizontal transfer CCD 18 so as to be outputted as an image signal.
In the photodetection device 4 as shown in FIG. 9B, the color filters 9 are used to let light of a specific color enter each of the photodetectors 6. On the other hand, a photodetection device as shown in FIG. 12 is suggested, which uses a microprism 31 in order to disperse a light beam 30 coming from a photographic subject and passing through a microlens (not shown), and detects the light beams of respective colors of red (R), green (G) and blue (B) with photodetectors 32R, 32G and 32B (see Patent document 1).    Non-patent document 1: ‘Optical and Electro-Optical Engineering Contact’, vol. 40, No. 1 (2002), p. 24    Non-patent document 2: ‘Transistor Gijutsu’, February 2003, p. 128    Patent document 1: JP 2002-502120 A